Within the optimal thermal range, temperature fluctuations with similar means have little effect on offspring phenotypes: A comparison of two approaches that simulate natural nest conditions.

Temperature influences nearly every aspect of organismal function. Because aspects of global change such as urbanization and climate change influence temperature, researchers must consider how altering thermal regimes will impact biodiversity across the planet. To do so, they often measure temperature in natural and/or human-modified habitats, replicate those temperatures in laboratory experiments to understand organismal responses, and make predictions under models of future change. Consequently, accurately representing temperature in the laboratory is an important concern, yet few studies have assessed the consequences of simulating thermal conditions in different ways. We used nest temperatures for two urban-dwelling, invasive lizards (Anolis sagrei and A. cristatellus) to create two egg incubation treatments in the laboratory. Like most studies of thermal developmental plasticity, we created daily repeating thermal fluctuations; however, we used different methods to create temperature treatments that differed in the magnitude and breadth of thermal cycles, and then evaluated the effects of these different approaches on embryo development and hatchling phenotypes. Additionally, we measured embryo heart rate, a proxy for metabolism, across temperature to understand the immediate effects of treatments. We found that treatments had minimal effect on phenotypes likely because temperatures were within the optimal thermal range for each species and were similar in mean temperature. We conclude that slight differences in thermal treatments may be unimportant so long as temperatures are within a range appropriate for development, and we make several recommendations for future studies of developmental plasticity.

Embryos of non-native anoles are robust to urban thermal environments.

The transformation of natural habitats into urban landscapes dramatically alters thermal environments, which in turn, can impact local biota. Ectothermic organisms that are oviparous are particularly sensitive to these altered environments because their embryos cannot behaviorally thermoregulate and the surrounding environment determines the temperature experienced during development. We studied the effects of urban and forested thermal environments on embryo development and hatchling phenotypes in two non-native lizards (Anolis sagrei and A. cristatellus) in metropolitan Miami, Florida. To determine if embryos from urban and forested sites are adapted to their respective thermal environments, we incubated eggs from each site using temperatures that simulate likely nest conditions in both urban and forested environments. For both species, urban thermal environments accelerated embryonic development, but had no impact on egg survival or any of the phenotypic traits that were measured (e.g., body size, running performance, and locomotor behavior). Our results provide no evidence that embryos from urban and forested sites are adapted to their respective thermal environments. Instead, the lack of any major effects suggest that embryos of both species are physiologically robust with respect to novel environments, which could have facilitated their success in establishing in non-native ranges and in human-modified landscapes.

Morphological evolution and niche conservatism across a continental radiation of Australian blindsnakes.

Understanding how continental radiations are assembled across space and time is a major question in macroevolutionary biology. Here, we use a phylogenomic-scale phylogeny, a comprehensive morphological dataset and environmental niche models to evaluate the relationship between trait and environment, and assess the role of geography and niche conservatism in the continental radiation of Australian blindsnakes. This fossorial snake group comprises 47 described species and is widespread across various biomes on continental Australia. Although we expected blindsnakes to be morphologically conserved, we found considerable interspecific variation in all morphological traits we measured. Absolute body length is negatively correlated with mean annual temperature and body shape ratios are negatively correlated with soil compactness. We found that morphologically similar species are likely not a result of ecological convergence. Age-overlap correlation tests revealed niche similarity decreased with relative age of speciation events. We also found low geographical overlap across the phylogeny suggesting speciation is largely allopatric with low rates of secondary range overlap. Our study offers insights into the eco-morphological evolution of blindsnakes, and the potential for phylogenetic niche conservatism to influence continental scale radiations.